An important example of application of the components in question here are so-called IMUs (inertial measurement units) including a MEMS element, which includes both a rotation rate sensor component and an acceleration sensor component. The two sensor components are implemented in the layer structure of the MEMS element and are situated side by side. They are capped with the aid of the second element in order to protect the sensor structures and to ensure defined pressure conditions for the particular sensor operation. Since rotation rate sensors and acceleration sensors are usually operated at different ambient pressures, a separate cap structure is provided for each sensor structure in the second element. In the case of rotation rate sensors, one part of the sensor structure is driven resonantly. A low internal pressure of approximately 1 mbar may be therefore set in the cavity of a rotation rate sensor element in order to keep damping of the sensor structure low. The rotation rate sensor may then be operated even at a relatively low excitation voltage. In contrast thereto, the sensor structure of an acceleration sensor should not be excited to vibrations. Acceleration sensors are therefore operated at a significantly higher internal pressure of typically 500 mbar.
Patent document US 2012/0326248 A1 relates to the implementation of such different pressure conditions for the individual sensor components of a MEMS element which are capped with the aid of a shared cap element. This publication suggests, among other things, that the bonding process used to bond the MEMS element and the cap element shall be carried out in multiple stages, so that the cavities of the individual sensor components are not sealed simultaneously but instead are sealed in successive bonding steps. This procedure makes use of the fact that the external pressure conditions during a bonding process may vary greatly. It is therefore possible to predefine different pressure conditions during the successive bonding steps and to select them in accordance with the sought internal pressure of those cavities, which are sealed in the particular process step.
According to patent document US 2012/0326248 A1, the pressure-tight connection between the MEMS element and the cap element is established via two layers of material, which are applied to the two element surfaces to be joined and out of which bonding frames for the individual cavities are structured. To achieve a multistep bonding process, the bonding frames for the individual cavities are created with different layer thicknesses on at least one of the two element surfaces.
During the bonding process, the MEMS element and the cap element are pressed against one another with the surfaces thereby prepared. The thickest, most exposed bonding frames then come into contact initially and, in a first bonding step, form a hermetically sealed bonding connection by which a first cavity is sealed. The elements are then pressed together until the thinner bonding frames also come into contact. Only then is an additional cavity sealed by the resulting hermetically sealed bonding connection of the thinner bonding frames. Since this second bonding step is carried out at a different ambient pressure than the first bonding step, different internal pressures are established in the two cavities.
The manufacture of bonding frame structures having different layer thicknesses has proven to be relatively complex in practice and is not suitable for all bonding materials.